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1 ELECTROPHORETIC STUDIES OF 

TURBIDITY REMOVAL BY COAGULATION 
J WITH FERRIC SULFATE 



By 
JAMES VERNON WALTERS 



J 



A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF 

THE UNrVERSITY OF FLORIDA 

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE 

DEGREE OF DOCTOR OF PHILOSOPHY 



UNIVERSITY OF FLORIDA 

August, 1963 



ACKWOl^IEDG^lENTS 

The author wishes to express his gratitude to his coinmittee 
chairman, Dr. A. P. Black, for giiidance and encouragement he has given 
during the investigation and for his generosity in the giving of him- 
self to his students. He deeply appreciates the friendship and help- 
fulness of Prof. J. E, Kiker, Jr., Prof. G. B. Morgan, Jr., and Prof. 
T. deS. Furman, members of his supervisory committee, xvho have helped 
him in many ways during his graduate study at the University of Florida. 
Dr. T. R, Waldo, of his supervisory committee, has generously given her 
time to guide the author in his dissertation preparation. He gratefully 
^ acknowledges his indebtedness to her. 

Dr. Horihito Tanbo's sketch of the Briggs cell which is included 
herein, will remind the author of the hours of consultat-ion Dr. Tanbo 
gave him. Mrs. A. L. Smith, Dr. R. F. Christman, and Dr. S, A. Hannah 
have also given the author the advantage of their experiences in water 
coagulation research. The author tharJcs Mrs. J, G. Larson, Mr. ¥. T, 
Halters, and Mr. C. Chen for their help in the execution and reporting 
of his experiments. 
\ The research was directly supported by VJater Supply and Pollution 

Control Research Grant WP-139 from the Public Health Ser^/ice, and was 
indirectly supported by Ford Foundation loans and Public Health Service 
Traineeships which financed the author's graduate study. 



ii 



The author shall forevermore tr^,'- to express his appreciation and 
gratefulness to his sons and his wiies Barbara, whose love and under- 
standing have sustained him. 



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X2.-J. 



CONTENTS 

Page 

ACKNOVJLEDGMENTS ,.....« ii 

LIST OF TABLES vi 

LIST OF FIGURES vii , 

CHAPTKR 

I. INTROUJCTION 1 

II. HISTOHia^L REVIE/J 3 

III. COAGULATION THEORY . H 

r/. PURPOSE Aira SCOPS ......... • 2^ 

V. EX?ERIi4EI^TAL MATERIALS AND PROCEDURES ....... 26 



26 
26 
26 



Ma.t.eria.ls »«....».«....••»»••• 
ClSLys »...»..»•.»..•••••••• 

Ferric Suli'ate ...»..•».«*<»••••• 

Procedures .«...». ..««.*•*••♦«■* 2o 

Preparation of Clay Stispensions .,.....» 28 

Preparation of Ferric Sulfate ......... 29 

Coagulation Tests .».«....♦»•.•*• 3^ 

Saraple Preparation .».»....»*<>»«• 3^ 

Flocculation .»•..»...»..•»••* .5— 

1 Initial and Residual Turbidity Measurements . 32 

! Residual Iron Determinations • 32 

! Measurement ofpH 33 

Electrophoretic Mobility Determinations 33 

Dosing and Mixing ....«». 33 

I ■'' Conductance Measurement «..«...«».. 3"^ 

■^ Measurement oipH • 3^ 

J Particle I-bbility Measurement ........ 3^ 

VI. DISCUSSION OF RESULTS 3S 

VII. CONCLUSIONS . • 76 

APPENDIX ..,..........»»•«•••• 7° 



XV 



Page 

BIBLIOGRAPHY . « « 102 

BIOGRAPHICAL SKETCH 10? 



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LIST OF TABLES 

Table Page 

1. Analysis of Feirric Sulfate Used for Coagulation ... 27 

2 . Properties of the Clay Suspensions .......... 38 

. 3* Coagulant Dosages 39 

k. Effect of pH on Electrophoretic Mobility and 

Sedimentation of Montraorillonite Clay 79 

5. Coag-alation of Montmorillonite Clay Hith 3.O 
Milligrams Per Liter of Ferric Sulfate 80 

6. Coagulation of Montmorillonite Clay With 5.0 
Milligrams Per Liter of Ferric Sulfate 83 

7. Coagulation of Montmorillonite Clay With 50 
Milligrams Per Liter of Ferric Sulfate 85 

8. Effect of pH on Electrophoretic Mobility and 
Sedimentation of Faller's Earth ....".,..... 87 

9. Coagulation of Fuller's Earth With 3.O Milligrams 
Per Liter of Ferric Sulfate ..... 89 

10. Coagulation of Fuller's Earth V/ith 5.O Milligrams 
Per Liter of Ferric Sulfate 91 

11. Coagulation of Fuller's Earth With 50 Milligrams 
Per Liter of Ferric Sulfate ... ..... 93 

12. Effect of pH on Electrophoretic Mobility and 
Sedimentation of Kaolinite Clay ..... ^k 

\ 13. Coagulation of Kaolinite Clay With 3.O Milligrams 

■^ Per Liter of Ferric Sulfate ...... 95 

l^'. Coagulation of Kaolinite Clay With 5.O Milligrams ; 

Per Liter of Ferric Sulfate 97 \ 

15. Coagulation of Kaolinite Clay With 50 Milligrams 

Per Liter of Ferric Sulfate 100 



vi 



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LIST OF FIGURES 

Figure Page 

1. The Helmholtz Layer Model 16 

2. The Gouy-Chapman Diffuse Layer Model. 18 

3. The Stem Layer Model 20 

-4-. The Briggs Cell 35 

5. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: 0,0 mg/l .... 42 

6. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: 3«0 mg/l . . . ,. ^ 

7. The Effect of pH and Mobility upon Coagulation, Clay: 
Mofifensriilsfiltg Fefj*iss Sulfate DsaagiSi $»Q pig/l . , « » k$ 

8. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: 50. mg/l .... k-6 

; 9. The Effect of pH and Mobility upon Coagu.lation. 

Clay: Montmorillonite k-8 

10. The Effect of pH and Mobility upon Coagulation. Clay: 
Paller's Earth Ferric Sulfate Dosage: 0.0 mg/l .... k-9 

11. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 3.0 mg/l .... 50 

12. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 5-0 mg/l .... 52 

13. The Effect of pH and Mobility upon Coagulation. Clay: 

J Fuller's Earth Ferric Sulfate Dosage: 50. mg/l .... 53 

Ik. The Effect of pH and Mobility upon Coagulation. Clay: 

Fuller's Earth . , 54- 

15. The Effect of pH and Mobility upon Coagulation. Clay: 

Kaolinite Ferric Sulfate Dosage: 0.0 mg/l 55 

■ 16.. The Effect of pH and Mobility upon Coagulation. Clay: 

Kaolinite Ferric Sulfate Dosage: 3«0 mg/l 5^ 



vii 



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Figure Page 

17. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinite Ferric Sulfate Dosage: 5.0 mg/l 57 

18. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinite Ferric Sulfate Dosage: 50. nig/l 58 

19. The Effect of pH and Mobility upon Coagulation. 
Clay: Kaolinite 59 

20. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 3.O mg/l , 51 

21. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 5.O mg/l 62 

22. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 50. mg/l ..... 63 

23. The Effect of pH on Iron Residual. Clay: Fuller's Earth 
Ferric Sulfate Dosage: 3.O mg/l (^ 

2^. The Effect of pH on Iron Residual. Clay: Fuller's Earth 

Firrio Sulfat© Dosages 5.0 mg/l ..,..,., 65 

J 25, The Effect of pH on Iron Residual. Clay: Fuller's Earth 

Ferric Sulfate Dosage: 50. mg/l ............. eS 

26. The Effect of pH on Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 3.O mg/l ..... 67 

27. The Effect of pH on Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 5.0 m.g/l 68 

23. The Effect of pH on Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 50. mg/l ..... 69 

29. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth ............. 7I 

30. Quantities of Acid or Base Required for pH Adjustment 

) of Fuller's Earth ■^2 



o 



31. Quantities of Acid or Base Required for pH Adjustmen 
of Fuller's Earth , , 03 

32. Qxiantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth 74 

33. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth 1 . . 75 



•'J2.-^:l 



I. INTRODUCTION 

Clays are the most common source of turbidity in surface -waters 
J ■ . ' used for municipal and industrial water supplies. Before surface water 

is satisfactory for domestic and industrial use, most of the clay and 
other particulate matter present in the water must be removed. Removal 
of the suspended matter is usually accomplished by alum or ferric sul- 
fate coagulation, sedimentation, and rapid sand filtration. Water 
treatment plants -which utilize this process produce finished waters > 
xdiich regularly exceed the minimum quality required for potable water 
by th© U. S. Public Health Service.*^' ^'-^ The specif io Public Health 
\ Service recommendation concerning turbidity is that the turbidity of 

drinking water be less than five units. 

Prediction of the optimum coagulation conditions for the produc- 
tion of such high quality water from a given raw water is very diffi- 
cult. In the absence of records of previous treatment of x^ater from 
the same source it is rationally impossible at present. The difficulty 
of coagulation prognosis is the resiilt of complexly related effects of 
the numerous properties of the raw water and the chosen coagulation 
conditions which affect the efficacy of coagulation. Among these con- 
ditions and properties are: specific coagulant chosen; coagulant dosage; 
pH, alkalinity, ionic constituents, and base exchange capacity of the 
raw water; and size, shape, chemical nature, hydration, and charge of 
the colloidal particles in suspension. Most of the factors vMch affect 
coagulation also affect the electrophoretic mobility of the suspended 

- 1 - 



J/ 



- 2 - 

colloidal particles. 

Electrophoresis is the movement of electrically charged particles, 
suspended in a conducting liquid medium, -vAiich results from the impres- 
sion of an electric field, ELectrophoretic mobility is the ratio of 
the speed of electrophoretic movement to the intensity of the elec- 
J trical field -Kfcich produced the motion. It is commonly expressed in 

microns per second per volt per centimeter. 

Mineral content, coagulant, coagulant dose, alkalinity and 
nature of clay particles, of the numerous parameters vjhich affect elec- 
trophoretic mobility and coagulation, can be chosen and controlled for 
a selected synthetic clay .suspension. In addition to these parameters 
v*ich can be selected, pH, base exchange capacity, effectiveness of 
coagulation and particulate electrophoretic mobility for a given suspen- 
\ sion can be directly measured. 

! The present research has been performed in order to study the 

: empirical relationships among electrophoretic mobility, residual tur- 

bidity, coagulant dosage, and residual iron (the mensurable parameter) 
I for the ferric sulfate coagulation of suspensions of three different 

I clays over the pH range between three and ten. To my loaowledge, such 

I a study has not been attempted before. The relationships discovered 

are described herein, and the effectiveness of ferric sulfate coagula- ■ 
tion of these clays is compared -with that of their alum coagulation, 
reported earlier by Black and Hannah, 



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II. HIST0Ria4L KSVIE/J 

The earliest records of the coagulation process have been traced 
by Black i&o torote: 

Although various crude methods of \^tec purification, generally .' 
characterised as coagxilationj have been kno^'n and used oince ^ . 
ancient tiixieSj knowledge of the fundamental factors invol.ved in 
the process has been acquired comparatively recently. 

The earliest references of scientific interest in coagulation as a 

process for the treatment of "trater are references to the trorks of 

D'Arcet '"^ and Jeunet. ' D'Arcet at the beginning of x.he nineteenth 

century and Jeunet in I865 sought to establish the v£.lue of the process, 

but it t-ras not used for the treatment of a public x-rater supply until 

1881» After its initiation in Bolton, England* the process ^v'as soon 

adopted in Eolland and in the United States. 

The first coagulation patent \^s granted j in 188^ j to Isaiah 
Smith Hyatt. ^ Folloiving the suggestion of Col. L. H. Gardner^ Superin- 
tendent of the New Orleans Water Company* Hyatt successfally treated 
turbid x^rater by combining the use of perchloride of iron as a coagu- 
lant vn.th his process of rapid filtration. His patent covered not only 
the use of perchloride of iron, but also of "any other suitable agent 
v^ich is capable of coagulating the impurities of the liquid and pre- 
venting their passage through the filter bed," 

The 188^!- Ar.nual Re-port of ^le State Geologist of New Jersey con- 
tained results of tests of various salts as coagulants. Austen and 
Wilber^'^ concluded that of the salts investigated, aluminum sulfate 
was most effective. Puller-^° published a description of similar studies 

- 3 - 



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> ^i- . 

in I898, He found sulfates of iron and aluminum to be most effective. 
The chloride of these elements followed next in order, bat their use as 
coagulants in vjater treatment has not developed on a practical scale. 

In the year of Fuller's publication, W, B. Ball,^ at Quincy, 
Illinois, began using a mixture of ferrous sulfate and lime for coagu- 
lation. Fourteen years later, E. V. Bull reported the first use of 

chlorinated copperas. This chsnical was not tried again until 1928, 

12 
•i&ien. Hedgepeth and Olsen used it for the successful treatment of a 

highly colored water. Ferric ion was produced by oxidation of the 
ferrous sulfate with chlorine. 

As use of the process has become prevalent, the number of re- 
searchers and the scientific disciplines they represent have prolif- 
erated. Black -^ and Packham in recent reviews of coagulation theory 
and related literature, thoroughly cover the many facets of historical 
and contemporary research, theory, and practice. The literature cited 
in the present study will consequently be limited to that directly 
, related to the research herein reported. 

In 1923 the first of a series of studies by Theriault, Clark, 

1^ 
and Miller was reported. The paper by Theriault and Clark described 

their trea-bnent of several buffered solutions with various amounts of 

alum to determine the effect of pH upon the rate of floe formation. 

They assumed that the optimum pH for coagxiLative treatment of viater 

vrould be the pH at vjhich the minimum time x-ras reqtiired for the formation 

of the aluminum floe. They found that generally the best floe formation 

occurred in the pH range ^.95 to 5»^« Higher alum doses resulted in 

broader ranges of pH over vdiich rapid coagulation was observed. These 

workers were unable to explain the difference between values of pH 



- 5- 
x-Aiich accompanied rapid coagulation in their study and the higher values 
observed to be most effective in "water treatment plants. 

In the same year, Baylis, using alvm to coagulate natural 

I 

waters of varying alkalinity, noted that for a given pH, vjaters of 
higher alkalinity required larger quantities of coagulant to accomplish 

y satisfactory treatment. For any chosen tjater he isas able to reduce the 

■ 

■ alum dosage hy adjusting the pH -with a strong acid, thereby neutral- 
izing a portion of the alkalinity originally present. The values of pH 

for optimum coagulation were in the range 5»5 to 7.0, 

-1 ^ 
Late in 1923, Miller published the second of the Theriault, 

Clark, and Miller papers. ■ He described their constituent study of pre- 
cipitates formed by the mixing of potassium alum solutions with sodiiom 
hydroxide solutions of various molarities. Although the anion concen- 
J tration of the coagulant had no practical effect, the amount of alkali 

; mixed with a given quantity of al-uminum exerted considerable influence ' 

I 

upon the composition of the precipitate. The ratio of aluminum to sul- 
fate ion was determined for the floe over the useful pH range, but the 
exact chemical nature of the floe i^xas not determined. His review of 
treatment plant records revealed that optimum coagulation occurred 
within the pH range 5.4 to 8.5. 

In another series of tests (1925) Miller ' investigated the 
effects of various anions upon the formation of floe in solutions of 
potassiiim alum. Generally, the anions of higher valence exerted 
greater influence upon coagulation, and~less alkali was necessary in 
their presences 

The composition of precipitates from ferrous and ferric salt 

-1 Q 

solutions was the subject of another 1925 publication by Miller. 



) 



- 6 - 
There precipitates from the iron salts were found to be very similar to 
floe from the analogous altrniintun salts, except that they were formed at 
pH values significantly lower than the minimum pH values observed for 
alxm floe and that they remain insoluble above the maximum pH at \±lch. 
alum floe exists. 

The results of Miller's experimental vrork allowed him to make 
three statements concerning the optimum conditions for floe formation 
with both iron and alumin-um coagulants, (l) There must be present in 
the water a certain minimum quantity of the metallic coagulant ion. 
. (2) There must be present an anion of strong coagulating power such as 
the sulfate ion, (3) The pH must be properly adjusted. 

In 1928 Bartow and Peterson ° examined the effects of various 
salts upon the formation rate for alum floe over the useful pH range, 
) Many of the salts studied increased slightly the rate of floe formation 

• and extended, on the acid side, the pH range over which floe occurred. 

In a paper published in 1928 and now regarded as a classic in its 

20 
field, Mattson described the coagulation of clay suspensions and the 

electrophoretic mobility measurement of clay particles as mobility was 

altered oj various dosages of aluminum salts. His work demonstrated 

the effect of the different anions and cations upon particle charge. He 

specifically predicted the utility of electrophoretic studies in water 

^ coagulation investigations and pointed out the predominant role played 

by the hydrated oxides formed during coagulation. 

In three articles Black and others^"'" ^^'^^ report investigations, 

made on a laboratory and semi-plant scale, of the effects of several 

anions upon the rate of floe formation for both aluminum and ferric 

salts. They proposed improved conditions for laboratory study of 



) 



- 7 - 
coagulation. Also they recommended the use of larger samples and con- 
tainersg constant stirring, and isohydric indicators. With such im- 
provements they could duplicate pilot plant results. Anions were found 
to be useful to increase the rate of coagulation and to broaden the pH 
ranges of rapid floe formation. The pH range for floe formation was 
wider for ferric sulfate than for alum, but no iron floe formed between 
pH values 6,5 and 8,5. The authors stressed the importance of adsorp- 
tion as an important mechanism of turbidity removal and also attributed 
zones of no floe fo3:*mation to a change in particle charge. 

In the slightly more than a decade since the publication of 
Black's 193^ article, the interest of water chemists seem to have been 
focused upon activated silica and other coagulant aids. The work of 

oh. o e 

Langelier and Ludwig * '^ marked the return of many researchers to the 
y field of basic coagulation theory. They initiated the use of synthetic 

clay suspensions and called attention to the importance of base exchange 
capacity and particle size distribution of raw water, the action of 
metallic hydrolysis products as "binders," and the occurrence of peri- 
kinetic coagulation. 

96 

In 1958, Pilipovich, Black, and others examined the relation- 
ships among pH, zeta potential, base exchange capacity, coagulant 
dosage, and turbidity removal for the coagulation of suspensions of 
five clays with alum. Clays of high base exchange capacity required 
considerably larger doses of coagulant to accomplish coagulation than 
did clays of lower base exchange capacity. The authors reaffirmed the 
superior effectiveness of hydrolysis products over that of trivalent 
aluminum ions as coagulating agents. 

Matijevic and others ' (I961) coagulated lyophobic colloidal 



- - 8 - 

suspensions of kno-wn particle charge and concentration vjith alvuninum 

nitrate to determine the nature of the species formed during alum floe 
formation. Results indicated that below pH 4 the simple trivalent 
hydrated aluminum ion prevails. Between pH 4 and pH 7 the probable 
j prevailing complex is the tetravalent AloCOH)^^. At higher pH values 

J the tetravalent hydrate is transformed into a divalent form -tiiich in 

turn yields to a complex of zero charge. 

In the same year Black and Hannah, using alum and various poly- 
electrolyte coagulants and coagulant aids, investigated the relation- 
ships among pH, electrophoretic mobility, base exchange capacity, coagu- 
lant dosage, and turbidity removal for the coagulation of three dif- 
ferent clay suspensions. Several equivalents of coagulant per equiva- 
Imt of clay base exchange capacity werg necessary to effect satisfac- 
; tory coagulation. The pH range of best coagulation was 7.5 to 8,5 in 

ifiiich range the electrophoretic mobilities of the clay particles was 
slightly negative. In some cases fair perikinetic coagulation occurred 
]. at pH values less than 4,5. 

In his study of the precipitation of aluminum hydroxide resrulting 
from addition of alum to solutions containing bicarbonate, carbonate, 
or chloride of sodium, Packham (i960) evaluated the degree of pre- 
cipitation by measuring soluble aluminum residuals and by photometrically 
1 recording turbidity of the system as a function of time. The maximum 

amount of precipitate was formed in the pH range 5,5 to 7,2, Maximum 
coagulation rate occurred between pH 7,2 and 7*6, and maximxam immediate 
precipitation was observed at pH 7,1 or 7,2, 

As his criterion of coagulation effectiveness, Packham chose the 
coagulant dosage required to reduce the initial turbidity by one-half 



^ 



- 9 - 

for a given set of conditions. The pH range he observed for optirram 
coagulation conditions based upon the use of this criterion does not 
agree mth the pH range for good coagxdation x-ihich others have reported. 
The difference results from the selection of different coagulation 
efficiency criteria. Use of Packh3in«s criterion to select conditions 
for coagulation in a treatment plant x-rould result in -prater of unsatis- 
factory quality. If he had chosen a much greater turbidity removal 
efficiency as his criterion, his prediction of optimum coagulation pH 
range would have coincided -with those commonly reported. 

Packham expressed the opinion that the coagulation of clay is 
principally accomplished by the enmeshment of the clay particles in the 
metallic hydroxide precipitate formed by reaction of the coagulants. 
Orthokinetie eoagolation is th© term now used to n^iie the mechanism 
he described, 

on 

Mackrle (I962) has presented arguments favoring tlae acceptance 
of the physical theory of stability and coagulation of colloidal clay 
suspensions. He has attached greater significance to the value of the 
psi potential, the potential difference between the "Helmholtz layer" 
and the bulk of the suspending mediura, than to the value of the zeta 
potential, the potential difference between the plane of shear and the 
bulk of the suspending medium. He has suggested that the metallic 
coagulants react to form crystalline hydrous oxide sols li^ch de- 
stabilize the clay suspension by mutual coagulation. His conclusions 
were based upon his xiork -with ferric sulfate and clay suspensions and 
upon crystallo graphic studies of such precipitates reported by others. 
In his tests pH and coagulant dose were allowed to vary simultaneously, 
and no measurements of electrophoretic mobility -were performed to 



- 10 - 

permit an examination of the independent relationships among pH, coagu- 
lant dosage, turbidity removal and zeta potential. 

In 1962 Sttrnim and Ihvgaxv^ cited the -work of others and identi- 
fied, for both iron and al-uminxim salts, the hydrolysis products of 
highest effective charge and assigned tentative formulae to them. They 

J also called attention to the aging effect of iron and aluminum sols and 

emphasized the chemical nature of particle charge caused by ionization 
as contrasted -with charge produced by physical adsorption. The majority 
of their laboratory tests were performed to determine the specific 
chemical interaction betvreen various functional groups normally found 
in ijater and the metallic .coagulants in common use. They concluded that 
metallic complexes other than hydrous o:3ddes can be formed as a result 
of the inttractions and that the interaction of the fimctional groups 

^ can appreciably affect the pH at i-jhich optimum conditions of coagulation 

occur. They also presented a method for carrying out laboratory jar 

i 

I tests at constant pH and convincingly justified the desirability of 

such a procedure. 



> 



in. COAGULATION THEORY 

Any explanation of coagulation theory must be preceded by a de- 
scription of the physical and chemical characteristics of the colloidal 
suspensions to be coagulated. The suspensions customarily encountered 
in the treatment of water for municipal and industrial use are dilute. 
Even -vhere raw water is taken from streams idaich carry heavy sediment 
loads, the water to be coagulated is dilute because presedimentation is 
used to remove the readily settleable particles. The materials vMch 
are removed from the dilute suspensions by coagulation can be generally 
classified as turbidity or "color." 

In their study of the nature of colored surface vjaters Black and 
Christman*^ have ascertained that "the materials responsible for color 
in water exist primarily in colloidal suspension in the water," They 
found particle size and number of particles to vary with pH, but particle 
size was generally less than 10 mn.. Although the present reseai*ch is 
not directly concerned with coagulation for color removal, color com- 
pounds do merit mention, because their colloidal nature and suscepti- 
bility to coagulation are similar to those of colloidal turbidity 
particles. 

The primary source of turbidity to which the present investiga- 
tion pertains is colloidal clay. Clays are complex aluminum silicates 
of sedimentary origin. Their lattice structures consist of layers of 
silicon-oxygen sheets and aluminum-oxygen sheets. These sheets, common 
to all clays, occur in different orders in the different classes of clays. 

- 11 - 



- 12 - 
Kaolinte, montmorillonite, and fuller's earth have been used in the 
present research. 

An important physico-chemical characteristic of clays ishich is 
considerably affected by the placement order of the sheets is base 
exchange capacity, Kaolinite and montmorillonite, of the clays used in 
y the present research, represent the low and high extremes of base 

exchange capacity -tiiich results from crystalline structure. 

Kaolinite consists of an alumina sheet and a silica sheet i/Mch 
are combined to form one layer, idiereas montmorillonite has an alumina 
sheet included between two silica sheets to form one layer. These 
layers have a definite thickness, measurable by x-ray diffraction 
methods, which is constant for a specific clay; but the lattices extend 
to the irregularly broken edges of the crystals in th© other tm direc- 
tions. In viater the parallel layers tend to split apart and become 
dispersed. Because of the small coulombic forces between similar 
adjacent silica sheets in montmorillonite, the surfaces of the layers 
become hydrated and therefore separate to a considerable extent. 
Kaolinite layers are held together tightly by hydrogen bonding between 
hydroxide ions on the bottom of one layer and oxygen ions on top of the 
- next layer and thus resist separation. A more detailed discussion of 
clay structure is given by Hendricks, -^^ 

Marshall and Krinbill"^^ have stated one of the results of the 
structural differences between kaolinite and montmorillonite. The base 
exchange capacity of kaolinite varies with particle size, vftiereas the 
base exchange capacity of montmorillonite is almost independent of 
particle size. 

Particle size is the property upon ■which the definition of 



^*^**c% aiifcr-i ■ iB^n a\^emt^m 



- 13 - 
colloids is based, but colloid behavior results from phenomena involving 
the tremendous surface area inherent in particles of colloidal size. An 
example of the importance of surface phenomena is that the classifica- 
tions of colloids, lyophilic and lyophobic, result from such a phenom- 
enon. Distinction between the two classes depends upon the wettability 
of the surface of the particle. The particles possessing poorly wettable 
surfaces are called lyophobic. Lyophobic colloids are vmstable, because 
by coalescing they offer a smaller surface area at which a solid-to- • 
liquid interface must be formed. Since the smaller interface results 
in a lower surface energy state and a lower total energy state for the 
system, the coalescence is spontaneous. 

Lyophilic colloids, on the other hand, are stable because of the 
attraction of the eurface for the solvent «- the wettability of the 
surface. These lyophilic colloidal solids which exhibit surface inter- 
action with the solvent are, therefore, the colloids of primary concern 
to water chemists. 

Another surface phenomenon which greatly influences the properties 
of a suspensoid is the electrical charge possessed by the particles. 
The charge can be initiated by several different surface mechanisms; 
still other surface phenomena affect charge magnitude and sign. 

Of the several mechanisms which can produce particle charge, we 
shall first consider the process that might be termed preferential 
ionization. As an example of this mechanism, we shall consider minute 
crystals of silver iodide in equilibrium with a saturated solution in 
which the ionic concentration product is roughly 10" . The force with 
which the two ions are held in the lattice differ greatly. Despite its 
larger size, the more polarizable iodide ion is held much more 



- 14 - . 

■ forcefully than is the silver ion. When the concentrations of the two 
I ions in the solution are equal, more silver ions escape into the solu- 

i 

tion than do iodide ions; hence, the crystals are negatively charged. 
If the silver ion concentration is increased, the charge can be reduced 

i _ to zero; a farther increase of silver ion concentration can cause a 

/ charge reversal, 

I Ionization of functional groups -tMch are connected to the 

particle by covalent bonds is a second and important source of particle 
charge. Examples of particles thus charged are proteins and ion 
exchange materials. Proteins are formed by long chains of amino acids 
joined by peptide linkages. Some of these amino acids carry an ad- 

I ditional carboxyl or amino group ■[■ihich can remain free and exposed to 

the solvent. Thus they can form COO and M^ ions x^aich are covalently 

I attached to the particle. The ion exchange materials are porous solids 

f 

] -tdiich have built-in acids or basic groups. The natural zeolites and 

many clays are included in this general category. 

Among the other mechanisms -which can cause particle charge are 

chemisorption and adsorption of specific ions resxilting from van der 

VJaal's forces. For particles vjhich are charged by the adsorption of 



;i specific ions, the surface charge density is greatly affected by concen- [ 

t 
i tration changes of those ions in the solution. i 

: I 

In all of the mechanisms mentioned above, particle charge was 
achieved by the separation of \inlike charges (the destruction of 
electroneutrality ) , Because of the large amount of energy involved in 
the separation of these charges, electroneutrality is disturbed only on 
the ultramicroscopic scale. When any one, or a combination of these 
mechanisms, produces an excess of charges of one sign in any locality, 



- 15 . 
there must exist an equal excess of charges of opposite sign in the 
immediate vicinity. Thus, we find surrounding and veiy near each 
charged particle an excess concentration of ions of counter sign. 
These ions are called counterions or gegenions. The counterion excess 
occurs only in the solution veiy closely surrounding each charged 
^ particle. Throughout the rest of the suspending medium electro- 

j neutrality prevails. 

I When we speak of electroneutrality and areas of excess charge, 

I we implicitly assume that the conditions we describe are the averages, 

with respect to time and space, of the several dynamic equilibria which 
prevail. Brownian movement is one spatial equilibrium which must be 
averaged. Ion exchange is a physico-chemical equilibrium of consider. 
■ able sffeot. Eaoh of the equilibria, ineluding these two, caus© 
fluctuations with respect to time. 

Based upon these averaged conditions, several models have been 
proposed to explain the possible arrangement of the charged surface and 
its surrounding array of counterions. These models have been used by 
chemists, physicists, and mathematicians as bases for their computation 
of theoretical values of parameters for many colloid systems. Probably 
none of the models proposed is correct, but each has been useful in 
the explanation of some observed phenomenon. 

The simplest of these was proposed by Helmholtz.^^ Fig. 1 is a 
. schematic section which shows the charged surface and the surrounding 
medium. By ionization or some other mechanism, the surface of the 
particle is charged. This excess of negative charge in or on the sur- 
face attracts toward the surface the positive ions in the solution. 
Helmholtz proposed a model in which all of the counterions so attracted 



- 16 - 



CHARGED 
SURFACE- 



PARTICLE 



r-HELMHOLTZ LAYER OF COUNTERIONS 



M 



te 

y 











;0;\va:v^:.0i 

-SURFACE OF SHEAR 




BOUND 
SOLVENT 



© 











© 



,.© 



© BULK OF 
SOLUTION 



< 



h- 
O 

a. 



DISTANCE 



FIG. 1 '-THE HELMHOLTZ LAYER MODEL 



- 17 - 
are located in a single surface parallel to and very near the surface 
of the particle. His model is analogous to a parallel plate condenser. 
The graph of potential in Fig. 1 represents the potential difference 
between the bulk of the solution and the point within the solid-liquid 
interface that corresponds vfith the abscissa. 

Fig. 2 depicts the Gouy-Chapraan^^ model v/hich is named for the 
two scientists who first considered it in detail. They recognized the 
Helmholtz assumption to be an oversimplification of the spatial 
arrangement of the neutralizing counterions. Reasoning that thermal 
agitation would prevent such an unifom arrangement of gegenions, they 
proposed a diffuse layer of variable but finite thickness which con- 
tains an excess concentration of counterions. In formulating their 
model they also considered the shielding effect of the counterions 
located near the particle upon the attractive force existing between 
the particle and the more distant counterions. The proposed model is 
characterized by a potential versus distance graph, for which the 
potential decreases at a decreasing rate as distance from the surface 
of the colloid increases. 

In addition to the gegenions which are attracted to the particle, 
a sheath of the solvent is tightly bound to lyophilic colloids. This 
sheath is pulled along with the colloid whenever some force such as 
that of gravity causes relative motion between the particle and the 
bulk of the solvent. Thus, there exists surrounding a colloid a surface 
of shear which contains the bound solvent that accompanies the particle 
as it migrates. 

If an electric field is impressed upon a colloid system, the 
colloids migrate toward the pole of opposite charge at a speed 



18 - 



CHARGED 
SURFACE- 



PARTICLE 



GOUY-CHAPMAN DIFFUSE LAYER 
^ — — f^ 

^ ©I ^ . 







@ 



® 


















© 


r^ ^ r\ ® BULK OF 
^ ^ SOLUTION 



© 

--^SURFACE OF SHEAR 



BOUND 
SOLVENT 



PSI POTENTIAL 




j N^^EJA POTENTIAL 

DISTANCE 



Fia 2 -THE GOUY-CHAPMAN 
DIFFUSE LAYER MODEL 



- 19 - 

proportional to the potential which exists between the surface of shear 
and the bulk of the solvent. (The "bulk of the solvent" refers to the 
portion of the solvent out of the effective interaction range of the 
charged colloids, that is, where electroneutrality occurs on micro as 
well as macro scale.) This shear surface potential upon which the 
velocity of a charged colloid in an electric field depends is called 
the zeta potential, 2 . The movement of the charged colloid that is 
caused by impression of the electric field is referred to as electro- 
phoresis; and the ratio of particle speed to the intensity of the 
electric field is termed electrophoretic mobility. In units commonly 
used for expression of mobility and potential, a Iji/sec/v/cm mobility 
is equivalent to a potential of I3 mv. 

Since th© valecity of colloid movement caused by a msasurabl© 
field intensity can be observed through an ultramicroscope or by 
moving-boundaiy frontal methods, the electrophoretic mobility of 
colloids is a directly measurable parameter. This parameter is closely 
related to particle charge, surface-charge-density diffuse-layer thick- 
ness, and particle surface potential, which are important parameters 
but are not directly measurable. (The surface potential,)^, mentioned 
above is diagramatically presented in Fig. 2),. 

A model suggested by Stem^^ represents further sophistication 
of the Gouy-Chapman diffuse layer theory. It includes the Stem layer 
of adsorbed counterions which are held in actual contact with the sur- 
face of the colloid. A section of the Stem model and a typical poten- 
tial curve for it appear in Fig. 3. In addition to the zeta potential 
and the surface potential,-}^ , the potential at the interface between 
the Stem layer and the Gouy-Chapman portion of the double diffuse 



- 20 - 



CHARGED 
SURFACE- 



r 



STERN LAYER 



PARTICLE - 



-^ 






E) 



■SURFACE OF SHEAR 



© © 
© 




BOUND 
SOLVENT 



BULK OF 
SOLUTION 



t 



< 

1— 

U 

O 

Q_ 



SI POTENTIAL-^^ 




■ZETA POTENTIAL 



DISTANCE 



FIG. 3 -THE STERN LAYER MODEL 



- 21 - 
layer is indicated and represented by the symbol'}^ . \ 

The models described above are useful as they provide a basis 
for appreciating the phenomena which influence the stability or insta- 
bility of a given colloidal suspension. The primary phenomenon favor- 
ing stability is, of course, the mutually repulsive force between 
similarly charged colloids. 

A particle with its complete double layer is electrically 
neutral, so that it exerts no net coulombic force upon another. This 
situation exists in the case of particles which are sufficiently dis- 
tant from each other. As two particles approach, however, the double 
layers interpenetrate and interact. Should the two particle surfaces 
finally touch, there could be no more diffuse layers between them to 
icr^in them from th© iff get of th® repulsivt coulombic feroe. It ia 
the work required to thus distort and finally destroy a part of the 
diffuse double layers which causes most of the repulsion. 

Charge density upon the particle surface and concentration of ■ 
ions in the solution surrounding a particle are parameters which 
directly affect stability. Low ionic concentration in the solution 
causes greater thickness of the diffuse layer. High charge density 
results in large psi potential. Thus low ionic concentration and high 
charge density contribute to colloid stability. The relationship of 
these parameters to zeta potential can be seen in Fig. 1. The con- 
ditions which contribute to stability result in high values of zeta 
potential; therefore, zeta potential, or more important, the directly 
measurable electrophoretic mobility can be a useful index of stability. 
A less important phenomenon contributoiy to stability is the van der 
Waal adsorption of similiions. This occurs to a significant degree 



- 22 - 

only under very specialized conditions, and the effect is more important 
with similiions of large molecular weight. 

The phenomena which are influential toward instability are much 
more numerous than those causing stability, because the foimer consist 
of all the phenomena which can impair the effectiveness of the latter. 
Of the instability mechanisms, the two most important are the mutual 
attraction (and coagulation) of oppositely charged colloids and the van 
der Waal attraction. The other mechanisms are of much less direct 
importance, or they effect instability through their influence upon or 
in conjunction with one of the two mechanisms mentioned. 

Van der Waal forces' are alxjays attractive; but because they 
result from dipole interaction, they decrease approximately with the 
third power of the distance betv;een the particles. Thus they are 
effective only when the particles are brought into extreme proximity. 
Coulombic forces between similarly charged colloids oppose their 
approach toward each other with force which decreases roughly with the 
second power of the distance between the particles, so that some other 
force is required to push them close enough together for van der Waal 
forces to prevail. Brownian motion caused by thermal agitation is one ■ 
source of such force. Mechanical agitation of a suspension can 
simi3^rly contribute to -instability. 

Some other factors effect instability by reducing the particle 
charge or potential of the colloids. The concentration of "potential 
determining ions" in the solution exerts a large influence upon this 
parameter. The hydrogen ion concentrations will determine the charge 
density and, hence, the potential of any particle which depends upon 
the ionization of carboxyl or amino groups as its source of charge. 



- 23 - 
The concentration of inert ions in the solvent can affect stability by 
increasing the probability of particle collisions as their niimber is 
increased and by causing compaction of the diffuse layer. 

Ionic concentration is not the only ionic variable which 
influences stability. The valence and size of the specific ions present 
exert effects upon particle charge and potential. The Schulze-Hardy 
rule is a general statement of the observed phenomena that divalent 
counterions are more potent in the production of instability than mono- 
valent counterions and that trivalent ions are much more powerful coagu- 
lation agents than the divalent counterions are. Ion size and less 
important anomalous characteristics of specific ions influence their 
ability to cause colloid instability as is evidenced by the Hoffmeister 
series in which various anions and cations have been listed in order of 
flocculating power. 

Because of the numerous mechanisms which are responsible for 
de stabilization, the many variables which affect stability, and the 
differing chemical and physical nature of the sundry colloidal particles 
which may be encountered, it is practically impossible to calculate the 
conditions under which satisfactory coagulation of a given colloidal 
suspension will occur. It is desirable, therefore, to examine the 
empirical relationships of the parameters that can be measured so that 
the work involved in cut-and-try coagulation can be reduced. 



IV. PURPOSE A1\TD SCOPE- 

The preceding chapters have re\aeued the raost significant work 
dealing with vjater coagulation and have siiianarized contemporary theoii.es 
concerning the basic mechanisras involved. Because of the complexity, of 
relationships among the n-aniberous variables X'jhich affect coagulation,' 
many researchers have sought to discover empirical relationships among 
the measurable parameters in order that they might more fully understand 
basic coagoilation mechanisms , 

Black and Hannah i, Pilipovich and others.; Black and WillemSj 



'5 



and Black and Christman have pursued such a course in the electro- 

phoretic studies of the coagiilation of several colloidal materials vri.th 

39 29 

various coagailants and coagulant aids. Packham-^ and Kackrle have 

reported some ferric sulfate coagulation research, but neither of them 
performed electrcphoretic studies of coagulation in which the effects 
of coagulant dosage and pli have been separately determined. 

The primary puarpose of the present research is to add to the body 
of knowledge resulting from the work of Black, Hannah, Willems, Christ- 
man>j and Pilipovich: it vjill seek to learn the relationships among 
electrophoretic mobility, residual turbidity, coagulant dosage, and 
residual iron content of three clay suspensions resulting from their 
ferric sulfate coagulation. The three clays were chosen so that sus- 
pensions containing equal concentrations of them would exhibit low, 
medium, and high base exchange capacities respectively. The literature 
contains no references to vrork of this nature. 

- 2i^ - 



- 25 - 

Because certain materials and procedures i^rere utilized, the 
study, in addition to its primary purpose, will allow direct comparison 
of the results of ferric sulfate coagulation with the results of alum 
coagulation of these clays reported by Black and Hannah. Moreover, 
the results of these tests may yield experimental confirmation of coagu- 
lation theories previously presented by others. 

The scope of the work was limited to study of electrophoretic 
mobility, residual turbidity, and residual iron content in the ferric 
sulfate coagulation of suspensions of a low, a medium, and a high base 
exchange capacity clay over the pH range 3 to 10. The ferric sulfate 
dosages were 0, 3, 5, and 50 mg./l respectively. The procedures 
involved xjere jar tests, residual turbidity and iron determinations, 
and electrophoretic mobility determinations. 



V. EXPEKQ'IENTAL MATERIALS AND PROCEDURES 

The experimental portion of the research consisted of (1) jar 
tests for the ferric sulfate coagulation of three clay suspensions and 
(2) the determination of mobilities for the flocculating colloids in 
those suspensions. Coagulant dosages of 0.0, 3.0, 5.O, and 50 rag/l of 
ferric sulfate were used, and pH was varied over the range 3 to 10. 
Final dissolved iron content, final pH, and initial and final turbidity 
of the jar test suspensions were measured, and pH values of mobility 
samples were determined. 

Materials 

Clays 

The clays used to prepare turbid waters were Kaolinite 4 and 
Montmorillonite 23, obtained from Ward's Natural Science Establishment, 
and fuller's earth, obtained from the Floridin Company. 
Ferric Sulfate 

The ferric sulfate used as coagulant was the commercial grade 
manufactured by the Tennessee Corporation, Atlanta, Georgia. Ferri-Floc 
is the registered trademark by which the manufacturer designates this 
material. The analysis of the particular sample of ferric sulfate used 
appears in Table 1. 



- 26 - 



- 27 - 



TABIE 1 
ANALYSIS OF FERRIC SULFATE USED FOR COAGULATION 



Constituent Per Cent by Weight 



Total ¥ater Soluble Iron 21.50 

¥ater Soluble Ferrous Iron (Fe-H-) O.7O 

Water Soluble Ferric Iron (Fe-H-f-) 20.80 

Water Insoluble Matter 2.00 

Free Acid (as HgSO^) 2.55 

Moisture 2.5I 



- 28 - 



Procedures 



Preparation of Clay Suspensions 

Hannah has given the following description of the clays used 

and of the first steps in their preparation: 

The kaolinite and raontmorillonite consisted of large lumps of 
diy clay. These materials were crushed and groujid with mortar 
and pestle and were then ball-milled for Zk hours. The fuller's 
earth, vrhich was obtained as a dry povrder, was ball-milled for 
24 hours. 

The preparatory efforts of others, described above, were performed 

early in 1959- At that time Hannah determned the base exchange [' 

capacity of each of the three clays in the manner prescribed in Official 

Methods of Analysis of the Association of Official Agricultural 

4-1 
Chemists . Since their preliminary^ preparation the dried clays had 

been stored in closed glass containers. With the clays in the condition 

described, the present experiment was begun x^rith the weighing out of 

four 3'75-g aliquants of each clay. Each aliquant, in turn, was mixed 

x^fith 500 ml of demineralized xjater and dispersed by mixing in a Waring 

Blendor for five minutes. The four aliquants of each clay suspension 

were placed in a separate covered beaker and allowed to hydrate for 24 

hours. At the end of the hydration period, each suspension was slowly 

passed through a sodium-cycle, ion-exchange column to replace the 

natural, exchangeable cations of the clay with sodium ions. A glass 

column of 25 mm diameter contairiing a 12 -inch depth of Nalcite HCR 

cation-exchange resin was used for the ion exchange process, which was 



* 
The Waring Blender is manufactured by Waring Products Company, 
New York, Kex-r York. 



- 29 - 
developed by Lewis. Just before the treatment of the three clay sus- 
pensions the resin in each was regenerated with one liter of ten per 
cent KaCl solution. 

Stock suspensions were prepared by diluting each of the three 
suspensions to twenty liters with demineralized water. The three sus- 
pensions were stored in polyethylene carboys. 
Preparation of Ferric Sulfate 

A 2-kg portion of commercial-grade ferric sulfate was taken from 
a 100-lb bag of the material which was supplied by the manufacturer. 
After being mixed thoroughly, the sample was quartered, and 500 g were 
reserved for analysis. Approximately 100 g of the remaining material 
was finely ground -with mortar and pestle. Aliquants of 1.000 g were 
weighed out and stored in glass vials having tight-fitting polyethylene 
stoppers . 

Because the hydrolysis reactions of ferric sulfate are dependent 
upon time and concentration, a fresh coagulant solution of the chosen 
concentration was prepared daily. One of the previously weighed 
aliquants x^as quantitatively transferred to a 200-ml volum.etric flask, 
which was then filled to the mark with demineralized water. This par- 
ticular concentration was chosen, because less concentrated solutions 
became cloudy and x-jere found to contain considerable volumes of hydro- 
lyzed material within four hours after the initial mixing. A minimum of 
twenty minutes was allowed for the mixing, which was accomplished with 
a magnetic stirrer. 



-30 - 



Coagulation Tests 

Sample preparation . After the preparation of the aforementioned 
clay suspensions, approximately six months passed before coagulation 
tests were begun. A high-speed mixer, equipped with a stainless steel 
shaft and propeller, was used to thoroughly mix the suspensions. The 
minimum time of mixing for any suspension was one hour. Mixing was con- 
tinued while 200-ml aliquants were pipetted into 8-oz polyethylene 
bottles. Also, triplicate 25-nil samples of each suspension were 
pipetted into beakers, and residue upon evaporation was determined for 
each in accord with the procedure specified in Standard Methods for the 
Examination of Water and Wastewater . ^ which hereafter will be referred 
to as Standard Methods . To provide an ionic concentration in the sus- 
pensions comparable to those of surface waters, 20 ml of 5.00-g/l sodium 
bicarbonate solution was added to each of the 200-ml suspension aliquants. 
In the final clay suspension samples, diluted as described below, the 
sodium bicarbonate concentration was 50 mg/l. 

In the morning of a typical day of coagulation tests, immediately 
after preparation of the coagulant solution, six of the 8-oz bottles 
containing the desired clay were selected, and their contents were 
quantitatively transferred to separate two-liter volumetric flasks in 
which 500 ml of demineralized water had been placed. Ten ml of chlorine 
solution containing O.^qo g/l of CI2 were pipetted into each flask. 
(During chlorine demand tests, that specific quantity had proved sxiffi- 
cient to satisfy the demand of the suspensions and still to leave about 
1 mg/l of free available chlorine to oxidize the ferrous iron present to 



- 31 - 
the ferric state. Such a prechlorination dosage is common for treatment 
of surface water.) Sufficient amounts of 0.1 N NaOH or HCl were added 
to the flasks to yield the desired pH of the final suspension, and the 
flasks were filled to the mark with demineralized water. A teflon- 
covered magnetic bar was placed in each flask, and the flask's contents 
were mixed for five minutes with a magnetic stirrer. One-liter gradu- 
ated cylinders were used to transfer half of each flask's contents to 
separate ii-S-oz square jars which were placed on the multiple laboratory 
stirrer (hereafter referred to as the jar test machine). The remaining 
contents of the flasks were retained for mobility determinations. 

Flocculation. The flocculation process was begun by rapidly 
stirring the suspensions while adding the correct coagulant dosage to 
each of the six suspensions. After receiving the coagulant dosages, the 
suspensions were mixed rapidly for 2 minutes and then slowly for 28 
minutes. Next the stirring paddles were removed, and the suspensions 
were allowed to settle for 10 minutes. The rate chosen for rapid mixing 
was 100 rpra. The speed initially selected for slow mixing was 40 rpm, 
but soon after laboratory tests were begun, 5 rpm was adopted for slow 
mixing since it appeared that higher rates might cause disintegration 
of the floccules. 

Promptly at the end of the sedimentation period 250-ml sajtiples 
were drawn from each jar. An apparatus similar to that described by 
Cohen x^as used to siphon each sample from approximately an inch below 
the surface of the supernant. The settled samples so obtained were 
used for residual turbidity and residual iron determinations. 



_P p-../''? six. jar, variable-speed stirrer used is a product of Phipps 
ana bd.Td, Inc., Richmond, Virginia. , 



In itial and residual turbidity Eeas-ax-ements . Turbidity of the 
samples \^2.s aieas'ared in a Lumetron Model ^-50 Filter Photometer. The 
procedure recoimnended by the manufacturer ■" required the preparation oi 
a calibration curare for each of the three clays used. Calibration for 
a single clay involved the preparation of eight to ten suspensions so 
that their turbidities uniformly covered the desired turbidity range. 
The optical density of each suspension >ras measured in the Luraetron.; for 
650-i3|i light over a 75»ma path;, Also, the turbidity of each of "che sus- 
pensions was detenrdned -i-rlth the Jackson Candle TurbidiKieter in the 

46 
manner set forth in Standard ^ Methods . 

Because coagulation efficiency t-jss to be judged upon the basis of 
turbidity removal, determination of irdtial turbidities t^ras necessary. 
An average value of initial turbidity for each of the three clay s-aspen- 
sions X'las obtained hj measaring the initial turbidity of the suspensions 
for the jar tests^ in which coagulant dosage w-as zero. 

Re sidual iron detex-'mination ^ The supernatant samples which were 
obtained in the manner described above were filtered prior to the deter- 
rflination of their iron content. A fine, smooth ^ quantitative filter 
paper^^ t-ias used. Filtration vsb.s necessary, because some of the iron 
present t-ras chemically or physically bound to floe particles of such 
small siae that they did not settle ou'c in the short settling period 
alloi^ied. In a vrater treatment plant the iron bound to such small 



*The L\imetron Photometer is a product of Photovolt Corp., New 
lorks KexT Tork. 

%.e paper used was paper No. 130^1 manufactured by VJill Corp., 
New Toi-k 52,, Ix^ew York. 



- 33 - 

floccules would not be foup.d in the finished v:ater, because sedimenta- 
tion of longer duration or passage through the rapid sand filter would 
renove thera. Filtration of the iron samples thus makes the laboratory- 
jar tests more nearly analogous to plant conditions. The iron content 
of several samples was determined x-iithout prior filtration. In a later 
chapter results of these determinations are identified and are compared 
with results for similar filtered samples. The variance of iron content 
between the two kinds of samples emphasizes the necessity for filtration. 

■ The phenanthroline method appearing in Standard Methods "^ was 
followed for the iron determinations. A 530-mM. filter and a 75-mi. light 
path were chosen for the Lumetron Model ii-50 Filter Photometer used for 
the colorimetric iron determinations. 

Measurement of pH . The final pH of the coagulated clay suspen- 
sions was measured with a Beckman Model G pH meter. 

Electrophoretic Mobility Deterainations 

Dosing and mixing. A period of four to eight hours usually 
elapsed after the final dilution of the clay suspensions before 
mobility determinations were made. In order to attain thoroughly mixed 
suspensions after the quiescent period, each suspension was stirred for 
five minutes on a magnetic stirrer just prior to the mobility deter- 
minations. The individual suspensions were dosed vixth. the appropriate 
amounts of coagulant at the beginning of the mixing. 



The Model G is a product of Beckman Instruments, Inc., Fullerton, 
California . 



- 3^- 
Condnc-t^ mee _ j n8a^suremerit«, Specific conductance was determined by 
the procedure described in Standard .. Methods » A Model RCI6BI Conduc- 

>!■ 

tivity Bridge vdth a pipette-form conductivity cell having a cell con- 
stant of 1 cm""" -was used for the measurements. 

Mgasy^j^eaent^^of _r)H« The pH of each suspension was measured im- 
mediately before the mobility of its particles t-jas deten-nined. A Beck- 
man Model G pH Meter was used for these measurements, 

^g; r ."& J^lg---^QMliti:measureiGent . Tae equipment and procedures used 
for the roicroelectrophoretic mobility determinations are those described 
in the paper by Black and Smith. '° The detailed description of the 
physical dimensions and construction methods for the glass cell appear 
m an article by Briggs,-" who designed it and for T-±iom it is named. 
Since both procedure and equipment are described in detail in the refer- 
ences citedj, only a general discussion of them mil be included here. 
In addition to the general account, however » any deviation from the 
suggested methods of Black and Smith xvlll be delineated specifically. 

The Briggs cell is constructed of Pyrex^ glass. Its rectangular 
cross- sectional shape and area are practically constant over the central 
portion of its longitudinal axis. A filling funnel is located at one 
end, and removable electrodes and outlet stopcocks are connected to 
either end of the cell. It is mounted in a metal stand wiiich holds it 
in proper position on the microscope stage and supports it yhen it is 
not in use. Fig. 4 is Tanbo's sketch^"^ of a Briggs cell. 



* 
The Conductivity Bridge is a product of Industrial Instruments, 
inc.. Cedar Grove j New Jersey. 

""Pyrex is a product of the Coming Glass Company, Midland, 

I-'iichipan* 



- 35 - 




_J 
-J 
LlI 
U 

00 

o 

L?J 



I 

Ll 



-36- 

Two Briggs cells were assembled, mounted, and calibrated before 
jar tests and mobility determinations were begun. Plastic Wood was 
found to be a more satisfactory packing material than any previously 
tried. If removal from the holder is ever necessary, the cell can be 
freed easily by soaking the assembly in acetone or a similar solvent. 

During the course of this study several improvements in technique 
were developed. (1) The cell holder was attached to the microscope 
stage with a pair of small clamps. This procedure prevented accidental 
misalignment of the cell during determinations. (2) Another deviation 
from the suggested procedure was the use of a ^-rara glass bead in each 
of the electrodes to prevent rapid mixing of the mercuric nitrate and 
potassium nitrate solutions in the electrode. This procedure was pro- 
posed by Briggs. (3) It was found that the mercuric nitrate solution 
could be introduced into the electrode most easily with a hypodermic 
syringe fitted with a 2-in needle, (if.) When sufficient mercuric nitrate 
solution was injected to bring the liquid level about 3 mm above the 
narrowest portion of the opening between the upper and lower chambers 
of the electrode, no trouble was experienced in placing the glass bead 
without entrapment of air bubbles beneath it. 

Serendipitously it was discovered that for the suspensions 
studied, electrodes prepared in the manner described above could be used 
over periods as long as a week. Moreover, for these particular suspen- 
sions it was possible to rinse the cell by passing demineralized water 
through it while it remained clamped in place on the microscope stage. 
The application of a low-intensity vacuum to the outlet tube caused 



* 
Plastic Wood is a product of Boyle-Midway, Chamblee, Georgia. 

/ 



- 37 - 
water velocity of sxifficient magnitude to remove the settled floccules; 
therefore, it was not necessary to remove the cell from the microscope 
stage more often than once a week. Once the system was aligned and the 
cell clamped securely in place, a check was necessary only at the begin- 
ning and ending of each day's determinations to be sure that the micro- 
scope was focused on the stationaiy layer inside the cell. The water 
aspirator which was used to pull cleaning water through the cell was 
also useful as an aid in filling the cell with a suspension without the 
entrapment of bubbles. 

The particle velocities were determined by visual observation 
and were timed with a stopwatch. A previously calibrated occular 
micrometer located in the plane of the microscope image of the station- 
aiy layer served as the measured course over which the flight of the 
particles were timed. The polarity of the electrodes was alternated 
between individual timings. Thus, of the twenty particles timed for 
each suspension, ten were observed to move toward the left, and ten 
moved toward the right. An exception to this characteristic movement 
was noted at the isoelectric point. At the isoelectric point various 
particles were observed simultaneously to move very slowly toward 
either electi-ode. The mobility of the particles of a suspension was 
computed from the mean of the time observed for each particle to travel 
a fixed distance; therefore, the computed mobilities are time-averaged 
rather than velocity-averaged mobilities. 



x'-L:J.OUiDii_'^J '^i 



Sorie physical charactoristias of tha clays i-jhich xjere •ased and 
tha procedures for preparation of the suspenaior-s studied have been 
d3seribed in preceding sections. Table 2 pressnts the turbidities, 
gravimetric concentrations » and base exchange capacities of these 



1 Li, ■jCy O o 



TArJUi 2 



i-cj^ijxiiiib On mil; oi_-.I bUb.:Ld'iblOj.\!S 



iitial 



Base Exchange Base Exchange 
Residue Upon Capacity of Capacity of 



Lsaj 



Turbidity nig/l 



Evaporation Glays 



ieq/. 



Suspensions 
^ieq/l 



Mcntjiorillcnite 58 
Fuller's Earth 79 

Kaolin! te 29i> 



62.0 



C-i-.O 



7i:'«0 



1,150 



265 



87 



71 «3 



6.^ 



Microequivalents X'Till be abbreviated P-eq, 



The base exchange capacities are important in relax.icn to ccagu 
-Lant dosages, Alsos the effects of coagulant dosage upon mobility and 
coagulation in the present study tjill be compared with sirtilar effects 
of coagulant dos-ge in the aluia coagulation study reported hj Hann 
_"c IS uesirabj-c;, "cnerefore.^ ohat the coagulant dosae"es used in both 



p. n . 



~ JO 



- 39 - 

investigations be expressed in terras corn.parable to the units of base 
exchange capacity eraployed herein. These expressions appear in Table 3' 

TABIE 3 
COAGULANT DOSAGES ■ 



Ferric Su?!.fat e^. Altai 

Big/l 't^eojl mg/l " M-eq/l 



3.0 3^ 5«0 k5 

5.0 57 15.0 135 

50.0 570 , 100,0 900 

Although norcdnal dosages of 5-0 ng/l -were included in both 
studies 5 the effective dosage of alusinura ion is considerably smaller 
than that of the ferric ion because water of hydration constitutes a 
larger portion of the arora dosage. Probably the most raeaningful compari- 
sons between the txm investigations can be siade for dosages of (1) 5.0 
mg/l of aluia ana 3»0 m.g/1 of ferric sulfate ^ (z) 5.0 rr.g/l of al-om and 
5.0 ffig/l of ferric sulfate , and (3) 100 lug/l of alum and 50 mg/l of 
ferric sulfate. These corabinaticns of dosages are not equals but the 
two lox^rer ferric sulfate concentrations bracket the lower alxira dosage j 
and the highest dosages of the ti:o studies represent concentrations 
greatly in excess of those necessary for good coagulation. 

The choice of a satisfactory criterion of good coagulation is 
particularly difficult. Adequate coag"alation must result in an ex- 
tremely high degree of turbidity reraoval. The optical property 5 turbid- 
ity,^ isus'G be relied upon as an index of reraoval efficiency. Use of this 



^ Zi-O - 
property is coiriplicated hj the effects of shape 5 size 5 number and. refrac- 
tive index of the particles responsible for the turbidity in a given 
sample . 

An example of the manifestation of these effects has been pre- 
sented in Table 2 » The suspensions contain equal gravimetric concentra- 
tions of the three clays, but the turbidities they exhibit are widely 
divergent. For water treatment plant operation a practical criterion 
comiTionly used requires that the turbidity of coagulated and settled 
water be five units or less. Such a cr-iterion is probably too stringent 
for use in this study because the short period of sedimentation xxTas 
insufficient for the settling of the srcaller particles v;hich contribute 
most to the tv.rbidity of a suspension „ Moreover., the selection of a 
specific residual turbidity as the criterion would be to recraire a much 
larger removal efficiency for the kaolinite suspension (initial turbidity: 
29^ units) than for the montmorillonite (initial' turbidity: 58 units) . 

Packham~ has arbitrarily chosen as his coagulation criterion 
that dosage which reduces initial turbidity by 50 V'^'^ cent„ This choice 
is undesirables because it differs so x-.\idely from acceptable conditions 
encountered in water treatment plant operation. Vie have arbitrarily 
chosen 90 per cent removal of initial turbidity as the criterion of 
satisfactory coagu.lation and results of the ti-;o studies Xv^ll be compared 
on this basis. 

The residual turbidities and particle mobilities for each permu- 
tation of clay and coagulant dosage have been gr-aphed as fxxnctions of 
pH. Both graphs for a single pertautation appear in the same fig-are. 
(The residual turbidities are expressed as percentages of the initial 
turbidity of each suspension.) Figures fs 6j 7s and 8 are based upon 



■"'— l/*'--^V*VWai^l*fc ^ IM»« 



„ ill _ 

the turbidity and mobility results for the montmorillonite suspensions 
x^-hich were treated vjith 0, 3, 5, and 50 mg/l of ferric sulfate respec- 
tively. 

In Figo 5 J pH is observed to exert minor influence upon ir^ont- 
iKorillonite mobility in the absence of any coagulant. Final turbidity 
is little affected by pH. Seine turbidity removal w-as accomplished by ' 
the agitation and sedimentation of the jar test procedure, bat the 
clarification so achieved i-jas not significant. 

Hannah's electrophoretic studies revealed that the mobility of 
the suspended clay alone vras relatively independent of pH, but the magni- 
tude of the mobilities he reported were appro:ximately 30 per cent smaller 
than those recorded during the present investigation.. The latter agree 

Jiraeh more closely Xvlth the raaxlmm negative clay mobilities reported by 

20 
Matt son and by others than do Eannah-So Such agreement can not be 

interpreted to be a proof of accuracy, because i-iattson» for example , 
TOrked with a different clay and did not report pH values. However, as 
consideration of figures below \-AH indicates the graph of the mobility 
versus pH for zero coagulant dosage does fairly well define the masijdum 
negative mobilities observable for the suspensions and coagulant under, 
consideration. In view of this relationship ^ comparison of mobilities 
for zero coagulant dosage x-Jith Mattson^s maxiraum negative clay m-obili- 
ties appears to be worthi-jiiile. 

The lack of agreement with Hannah's values led to a reconsidera- 
tion of the eq-uipment and procedure for mobility measurement. Of the 
mechanical devices ^jhich are used, the ammeter is the unit m^ost probably 
capable of introducing an error of such size and consistency. The pre- 
cision of the meters is about one or two psr cent of the full scale 



-42- 



r^K'K: ,W^'^c< "*' 




-- 2 3 4 5 6 

^120i 1 r — I r 



.o 



> 100 

Q 80 



cr 60 
_j 40 

< 

Q 20 

if) 
yj 



7 8 9 10 11 

120 




SLOW MIXING: 
40 RPM -o-Q- 

5 RPM -o-o- 



100 
80 
60 
40 
20 




2 3 4 5 6 7 8 



10 11 



FIG. 5. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
CLAY: MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 0.0 MG / L 



reading, and the accuracy is not likely to be as good as the precision. 
Vlhsn conditions such as the electrolyte conductivity or the available 
pov:er supply voltage make it necessar;,' to measure a current correspond- 
ing to only ten or fifteen per cent of the full scale readings the error 
involved in the determination may be si:-: to ten times as large as that 
for a reading at full scale. Perhaps the use of some more sensitive 
method of field intensity measurement circuitrj;- would allow closer 
agreement among the results of independent investigators. 

Fig. 6 shows the effect of pH upon mobility and turbidity removal 
of the ffiontmorillonite clay suspension for the ^~To.g/l coagulant dosage. 
Increasing pH was accompanied by a gra.dual increase in the magnitude of 
the negatixi-e mobility. The sasie trend was shoxai for Hannah's ^-rngjl. 
dosage, and^ as was previously mentioned, the magni-iv-ides of the mobili- 
ties x-jere only about ?5 psr cent of those from the present study. Ifcere- 
as the only good coagulation resulting from that alun dose was peri- 
kinetic coagulation at pH less than ij-Os 3-i^-g/l of ferric sulfate 
yielded good coagulation from pH 5 '5 to pH 6.6. 

With an increase of ferric sulfate to 5 ifig/l £s shown j-n Fig. 7? 
the Increase in mobility vjith increasing pH becomes greater j- although 
the curve is not so smooth. The most noticeable effect of the increased 
coagulant dose is the broadening of the zone of good coagulation over 
the range pK k-.S to 7.8. 

The 50-iGg/l ferr-ic sulfate dosage resulted in change reversal 
for values of pH less than 50* '^'^- Fig. 85 the algebraic decrease in 
mobility with increasing pH was observed again as it had been in the 
previous figures =■ Hannah^ s comparable alura dose of 100 mg/l resulted 
in a mobility curve of similar shape above pH k-^7i but the isoelectric 



^^ ;>yv 



- il4 - 




6 7 8 9 10 11 
pH 

FIG. 6. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION 
CLAY : MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 3.0 MG/ L 



-45- 



23456789 10 11 







10 11 
.120 



SLOW MIXING: 

40 RPM -a-a- 

5 RPM -o-o- 




100 
H80 
60 
40 
20 
O 



9 10 11 



FIG. 7 -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
C L AY : MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 5.0 MG / L 



- i^6 - 




> 1001- 
n 80 



^ 60 

40 



9 10 11 

120 



SLOW MIXING: 

40 RPM -o-D- 

5 RPM -o-o- 



Q 

hi O 




5 6 7 8 9 10 11 



2 



FIG. 8. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
C LAY : MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 50. MG/ L 



100 
80 
60 
40 
20 




- if? - 

point (pH 6.6) was considerably higher, and below pH k.6 as the solu- 
bility of aluiTxinuia increased the charge reversal effect of the alum also 
decreased. The alum dose resulted in good perikinetic coagulation be- 
low pH i!..5 and both alum and ferric sulfate produced good orthokinetic 
coagulation from pH S^S to 8.8 and from 5.5 to 10.0 respectively. 

Fig. 9 is a composite of the four preceding figures. It allows 
ready comparison of the broadening of the zone of good coagulation \n.th 
increasing coagulant dosage. Also the zone of perikinetic coagulation 
below pH 3,7 and the zone of poor or no eoag-alation from roughly pH -^ to 
pH 5 are easily identified. Probably the most important relationship 
graphically illustrated in, the fig-are is that the isoelectric point 
occuring at pK 5,3 for uhe one dosage causing charge re-.-arsal marks the 
beginning of the pH zone of most economical coagulation of the particu- 
lar clay and for the arbitral^ good coagulation criterion chosen. 

The next series of figures pertain to the coagulation of fuller's 
earth. Fig. 10 illustrates the effect of pH in the absence of coa,gu- 
lant. As was -ohe case ivrith montmorillonite , in the absence of coagu- 
lant, negative mobility increased vjith increasing pH value. Perikinetic 
coagulation occured below pH if .2 although no such coagulation had been 
observed for montmorillonite . 

Beginning with Fig. 11 3 the mobility curves become more complex 
as the varying effectiveness of the coagulants for charge reversal at 
different values of pH becomes more evident. For the 3-mg/l dosage 5 the 
original particle charge is reversed over a pH range of slightly more 
than one xanit. For this particular dose, comparison of mobility curve 
shapes for ferx-ic and alum coagulation are \!lrtually impossible because 
of lack of similarity. Good ferric coagulation was observed over the 



v;-V ?■ 



- is - ■ 



9 10 1 1 ■''" 
1G/L FE2SQ4)3 I ^ 




mn 



io. 9. -THb EFFECT OF p H AND 
MOBILITY UPON COAGULATION 
CLAY-: MONTMORILLONUE 



- 49 - 





3 4 
T r 



7 8 9 10 11 

120 



D 



D 




SLOW MIXING: 

40 RPM -D-D- 

5 RPM -K>-o- 



3 4 5 




6 7 8 9 10 11 
pH 

FIG. 10 -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 00 MG/ L 



-50- 




ri 2 3 4 5 

K i20r— T 



6 7 8 9 10 11 

120 




7 8 9 10 11 



FIG. 11. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION . 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 3.0 MG / L 



- 51 - 
pH range 5.6 to 7,3. 

When the ferric sulfate dose was increased to 5 mg/l (Fig. 12) 
the zone of charge reversal was increased to 3 pH tmits, and good coagu- 
lation occurred above pH 5.5. A most interesting effect noted in this 
particular portion of the study is the greater efficiency of 5 rpra slow 
mixing for perikinetic coagulation and the better orthokinetic coagula- 
tion that accompanied the ^0 rpm slovr mixing. 

■ The mobility curve for the 50-mg/l ferric sulfate dosage (Fig. I3) 
appears to be typical of excess ferric sulfate dosage for the three 
clays studied. Particles were positive below pH 6.3 » were isoelectric 
at that points and became increasingly negative as pH was raised to 10. 
The slope of the curve is steepest iniiiiediately above and belox-J the iso- 
iigiStris psiat ¥hi@h sltarly indiaatig a -mm q£ mMMosa stability, 
Hannah's comparable alum curve changes less abruptly at the isoelectric 
point, and the apparent effect of increasing solubility at low pH is 
evident. Ferric coagulation is good above pH 14-. 2. 

The composite graph for fuller's earth (Fig. l^i-) clarifies the 
relationship between the isoelectric point of the overdosed suspensions 
and the beginning of the zone of efficient coagulation. As was the case 
for montmorillonite, it appears that the "overdosed isoelectric point" 
does mark that beginning. Alsoj the broadening of the zone of good 
coagulation -with increasing dosage is evidenced. 

Individual mobility and turbidity graphs for the kaolinite clay 
are shown in Fig-ares I5, 16, 1?, and 18 ^ and Fig. 19 is the corresponding 
composite. The mobility curves are very similar to those for fuller's 
earth, and the comments above concerning the latter are qualitatively 
applicable. Regarding coagulation, the kaolinite is much more nearly 



-52- 



8 9 10 1 1 

r 




9 10 11 

120 



D D 

D 



SLOW MIXING: 

40 RPM -o— D- 

5 PPM 




3 45 6 78 9 10 11 



100 

-80 

-60 

40 

20 





FIG. 12. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION . 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 5.0 MG/ L 



- 53- 



9 10 1 1 
1 1 + 2 




5 6 7 8 



9 10 11 



FIG. 13. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 50 MG/ L 



- s^ - 



7 3 9 10 11 

T 




6 7 8 9 10 11 



RG. 14. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH 



' 55 ' 




3 



5 6 7 8 




9 10 1 1 

120 



SLOW MIXING: 
40 RPM 
5 RPM 




80 
60 
40 
20 



2 3 ' 



5 6 7 



10 11 







FIG. 15. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 



CLAY : KAOLINITE 

SULFATE DOSAGE 



FERRIC 
0.0 MG / L 



- 56 - 




1^- .^20 



7 8 9 10 11 

120 




6 7 8 9 10 11 
pH 

FiG.16. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
CLAY : KAOLINITE FERRIC 

SULFATE DOSAGE : 3.0 M G / L 



- 57 - 



9 10 1 1 




I— ^ 120 



9 10 11 

1 i120 




10 11 



FIG. 17 -THE EFFECT OF pH AND 

MOBILITY UPON COAGULATION . 
CLAY: KAOUNITE -FERRIC 

SULFATE DOSAGE: 5.0 MG / L 



-58- 



8 9 10 1 1 

1 1 s 1 ^ 2. 




9 10 11 



FIG. 18. -THE EFFECT OF p 
MOBILITY UPON COAGULATION . 
CLAY : KAOLINITE FERRIC 

SULFATE DOSAGE: 50. MG / L 



59 




! J ^ — ' . I ^ . i i i i__ i i j i \ 

MOBILITY UPON CGA 
CLAY : KAOUNITE- 









- 60 - 
similar to the montmorillonite . Most important, however, is that the 

"overdosed isoelectric point" near pH 6.0 marks the beginning of the 

52 
zone of good coagulation. Black and others have shown that the same 

relationship between the "overdosed isoelectric point" and the zone of 

good coagulation exist for the ferric sulfate coagulation of natural 

colored waters. 

An additional observation of possible importance concerns base 
exchange capacities of the suspensions. There was no observation of 
charge reversal in the present investigation for dosages for which the 
ratio of coagulant dose to base exchange capacity (both expressed in 
l^eq/l) was less than 1.0. .Good coagulation occurred for all three 
clays, hovTever, with a dosage of 3 Kig/l. For this dose the ratio men- 
tioned above for montmorillonite is O.i+Q, for fuller's earth is 2.0, 
and for kaolinite is 5<3> Work with ferric sulfate doses in a range 
which would yield ratios near unity should reveal more interesting 
information on charge reversal phenomena. 

The U. S. Public Health Service has set O.3 mg/l of iron as the 
maximum allowable concentration of that constituent in drirJcing water. 
In the present research, therefore, determination of the residual iron 
content in the supernatant was necessary in order that suitability of 
the various treatments could be evaluated. The results of the deter- 
mination are graphically presented in Figures 20 through 28. 

The most important information obtained from the iron determina- 
tion was that for all the pH zone of good coagulation, the residual iron 
content is below the maximum allowable concentration. Another interest- 
ing observation which is generally applicable for the ferric sulfate 
coagulation of the three clays is that residual iron values are less 



- 61 - 



9 10 11 



_j 



z 

O 



< 

Q 
(/) 

LlI 




9 10 11 



F1G.20.-THE EFFECT OF pH ON !RON 
RESIDUAL. CLAY: MONTMORILLONiTE 
FERRIC SULFATE DOSAGE: 3.0 MG/L 



- 62- 



_J 

o 

z 
O 



< 

Q 

CO 
LjJ 
DC 



1.4 

1.2 
1.0 

0.8 
0.6 
04 
02- 



0.0^ 



3 

T 



4 5 6 7 8 9 10 11 



^ 



FILTERED 
UNFILTERED-^^-^- 



^ 



^ 




1.4 
1.2 
1.0 
0.8 
0.6 
04 
02 



OO 



9 10 11 



pH 



FIG. 21. "THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: MONTMORILLONITE 
FERRIC SULFATE DOSAGE: 5.0 MG/L 



- 63- 



_J 

5 



o 



•mimJ 

< 

Q 
(/) 

tr 



1.4 
1.2 

1.0 
0.8 
0.6 
0.4 
0.2 



2 

r 



- 



0.0^ 
2 



3 



4 5 6 7 8 9 10 11 



FILTERED -0 0- 

UNFILTERED -)^— ^- 




^ 



1.4 
-11.2 
1.0 
0.8 
0.6 
04 



3 4 5 




9 10 11 



pH 



FIG. 22. -THE EFFECTOR pH ON IRON 
RESIDUAL. CLAY: MONTMORILLONITE 
FERRIC SULFATE DOSAGE: 50. MG/L 



- 64 - 



2 3 4 5 



O 



o 

QC 



< 

00 
UJ 
DC 



l.4r 

1.2| 

i.o[ 

Q8| 
0.6 
04 



7 8 9 10 11 



i1.4 
1.2 

1.0 
0.8 
-p. 6 
0.4 




9 10 11 



pH 



FIG. 23.- THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: FULLER'S EARTH 
FERRIC SULFATE DOSAGE: '3.0 MG/L 



- 65- 



_J 

o 
y 









Q 

CO 
LlI 



^L *^ 



5 6 7 



1.4 
1.2 
.0 



9 10 11 



FILTERED -0 0- 

UNFiLTERED -^— ^<~- 



1.4 
1.2 

1.0 
0.8 




^- - 



9 10 11 



pH 



FIG. 24. -THE EF 
RESIDUAL. CLAY: 
FERRIC SULFATE 



ECT OF pH ON IRON 

FULLER'S EARTH 
DOSAGE: 5.0 MG/L 



^ 66 ^ 



10 11 



5 






Q 

CO 
QC 




7 8 9 10 11 



pH 



FIG. 25.- THE EF 
RESIDUAL. CLAY: 
FERRIC SULFATE 



ECT OF 


pH ON IRC 


)N 


FULLER'S EARTH 




DOSAGE 


: 50. MG/L 



- 67- 



(D 






< 

Z) 
Q 




2 



3 4 5 6 



9 10 11 



FIG. 26- THE EFFECT OF pH ON IRON 

RESIDUAL. CLAY: KAOLINITE 

FERRiC SULFATE DOSAGE: 3.0 MG/L 



- 68 - 



O 



2 

o 



< 

Z) 



Lijfci 



1.2 



I. Or 



Q8 



L 



W 0.2 



0.0^ 



2 



3 4 5 6 7 




9 10 11 
T i il4 



7K 



FILTERED ■ -0 0- 

UNFILTERED -^^— ^- 



|1.2 

no 



^ 



^ 




0.4 



¥ ^ * J 



02 



9 10 11 



pH 



FIG. 27 -THE EFFECT OF 
RESIDUAL. CLAY: KAOLIN! 
FERRIC SULFATE DOSAGE 



pH ON IRON 
TE 

5.0 MG/L 



- 69 - 



8 9 10 11 



O 



,y' 






J 



3 



ftf 




9 10 11 



FIG. 28.- THE EFFECT OF pH ON IRON 

RESIDUAL. CLAY: KAOLINITE 

FERRIC sulfate' DOSAGE: 50. MG/L 



- 70 - 
than the inaximuia allox'^able concentrations in the lox^; pH range doi-m to 
pH 3.8. Furthermore, even at pH 3.O no supernatant contained more than 
1 mg/1 of iron in solution. These low residual iron values for clay 
coagulation are much lower than those reported for colored v:ater coagu- 
lation , 

Black and others-' have reported residual iron values for com- 
parable coagulant dosages in colored water that are six times as large 
as the largest observed in the present study for the same pH of 3.0. 
At pH values up to ^ or 5, the ratio was even larger. The difference in 
behavior of the clay and color colloids in this respect point out the 
need for a more thorough understanding of basic coagulation mechanisms. 

For the present research it vjas necessary to determine whether 
the pH of the samples employed for mobility determinations were identical 
mth the pH of the corresponding jar test suspensions. Figures 29 » 30s 
31, and 32 show the close agreement between the respective pH values. 
Fig. 33 is a composite of the four, which shows the effect of coagulant 
dosage upon the value of pH. It should be remembered that the suspen- 
sions which viere used were synthetic preparations containing 50 mg/l of 
sodium bicarbonate. A more poorly buffered solution might not yield 
such agreement between the two. Even i;-iith the systems used it \ias dif- 
ficult to dose the suspensions vjith the exact quantities of acid or base 
required to obtain evenly spaced mobility and turbidity curve points. 
Only the curves for fuller's earth are shoxra, since those for the other 
clays were similar. 



- 71 - 



n 



' I MOBIL! 
'^•^tlEST J 



SAMPLES 
RS -n— D- 



ES -<H>- 



1.2 
1.0 
OB 
0.6 
0.4 
0.2 
0.0 
02 




H 



FIG. 29.- QUANTITIES OF ACID 



OR BASE 



REQUIRED RDR pH ADJUSTMENT OF 
FULLER'S EART 



- 72 




2 3 



FIG. 30.- QUANTITIE 
REQUIRED FOR pH 
FULLER'S EARTH . 



S OF ACID OR BASE 
ADJUSTMENT OF 



70 



1.21 



(T T" 08h 



t 



0.6 

■Xna 

Lij 



MOBiLl 
"EST 



h- 



> 

3 






■ niirW 










FiG. 31. 

REQUIRED FOR 
FULLERS EART 



i I itio 



S OF ACID- OR BASE 



H ADJUSTMENT OF 



- 74 - 







50. MG/ L J, 



^o 



fiaiae 



O ^ 



RG.32. " QUANTITIES OF ACID OR BASE 
REQUIRED FOR pH ADJUSTMENT OF 

FULLER'S .EARTH . 



75 



.2F 



A 



p prpPir^ 



■Or 0.0 



"Al 



LlI 



UJ 
£L 

t/) 

H 
UJ 

i 





6 

o 



.or -^-0 
Q6h ^-^ 







FIG. 33. - QUANTITIES OF ACID 
REQUIRED FOR pH ADJUSTM 
FULLER'S EART 



OR BASE 
ENT OF 



VII . COKCLUSIONS 

In the present investigation, charge reversal at low pH was 
observed for all three clay suspensions when the ratio of coagulant 
dosage to base exchange capacity (both expressed in M-eq/l) exceeded 
three. With increasing pH the mobilities of these suspensions decreased 
until the isoelectric point (in the pH range 5-7) occurred. This 
"overdosed isoelectric point" was fo-ond to Eiark the beginning of the 
zone of efficient orthokinetic coagulation of all three of the suspen- 
sions studied. Such behavior has been reported for the coagulation of 

52 
colored water vjith ferric sulfate by Black and others. Furthermore, 

an analysis of the results of clay coagulation vrith aloiri i-eported by 

i{,0 
Hannah revealed that the "overdosed isoelectric point" was an indica- 
tor of effective coagulation conditions for those suspensions. 

The base exchange capacities of the suspensions studied were not 
found to be directly or proportionally related to the coagulant dosages 
required to effect satisfactor)!- coagulation j but they did significantly 
affect the coagulant dosages required to cause charge reversal at low 
pH. 

For all of the combinations of ferric sulfate dosages and clay 
suspensions studied, it was observed that in the pH zones of good coagu- 
lation the residual iron values were less than the maxiiriuia allowed in 
drinking water by the U. S. Public Health Service. Moreover, even at 

low pH the residual iron values were less (by a factor of six to ten) 

52 

than those reported by Black and others for the coagulation of colored 

- 76 - 



I iga ■i.iirifci>»'-tri 



APPENDIX 



- 79 



■P ^H -rj 
•H O "O 

a .H 
•H -P Xi 

f-i <D p; 
H 0) 

c 

^ CO 



H 

CO 

-P 



H 



00 















On 



\0 



On 












3- ^ 



^3- 






O 



CM 



CO 
t 

o 










o 'd 

© 
K -P 

I — i 

H pi P" 



!>i o 



-P' 

r-i- 

:^ 

o 



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iii 




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BIBLIOGRAPHT 



LITERATURE CITATIONS 

lo Public H ealth s ervjce Driiiking Water Standards. 1962, Pub* 956» 
USPHSj VJashingtciis D« Co (1^62 j a 

2, USPHS Drinking Water Standards , 1962, Federal PLegister (I^r. dj, 
1962). p. 2152» 

3, U« So Public Health Serviceo Drinking Water Standards, I96I, 
JG-o.r. BMA, 53J935 (^g» 196l)» 

4, Blacks, A„ Po aiid Hannah, S. A, Electrophoretic Studies of Turbidity 
Removal by Coagulation With Aluirinum Sulfate* Jourc AWi-IA , 53:438 
(Apr. 1961), 

5» Water Quali ty and Treat^iient ,, AWWA, New York , N. Y» (2nd ed» , 
19jo)„ p. 13I0 

6« Packham, R„ F^ The Theory of the Coagulation Process - A Survey 
of the Literature^ 2» Coagialation as a 'iater Treataient Process. 
ProCa of the. See o for Water Treatment . and Examination , il:106 
(19^2") . 

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the Nile and Water in General l-Jhich Holds Earthly Substances in 
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8« Jeunet, Ko Co j-ionit »__,S cio g 7<IQ^? (1865/ « 

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10c Fullers G« Wo Water Purifi c ation at Louisville . Van Kostrand Co., 
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12. Hedger5eth, L^ L« and Olsen^ W. C« Chlorinated Copperas - A New 
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- 104 - 

14a Theriault, E^J. ajad Clark, W. Mo i'-n Experimental Study ox the 
Relation of H' Concentration to the Formation of Floe in Alum 
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15^ Baylis, Jo R<, Use pf Acids With Alum in Water Purification and 

the Irfjportance of h"^ Ion Concentration. Jouro AVjWA, 10:365 (1923). 

l6« Fiiller, L. B„ On the Composition of the Precipitate From Partially 
All^alini zed Alum Solutions. Faho Health Repts », 38:1995 (1923) » 

l?o Fiiller s L» 3. A Study of the Effects of Anions Upon the Properties 
of MuiTx Floe. Fub« Health Repts., 40:351 (1925). 

l8o J'Uller, L. B, Some Properties of Iron Compo^ands and Their 

Relations to Water Clarification^ Fabo. Health Rspts » » 40:1413 
(1925). 

19. Eartow, E. and Peterson, B. F. Effect of Salts on the Rate of 
Coagulation and the Optimum Precipitation of Al-'on Floe, Indc, Eip:« 
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20. Mattsons S» J. Cata-ohoresis and the Electrical Neutralization of 
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21. Black, A» P.. Rics; Owen, and Bartow, Edi-rard. Formation of Floe 



by ALlminum' Sulfate. Ind. Sigo Cham.. 25:811 (1933)- 



22. Bar-cow, Sd^^rd^ Black, Ao P.» and Ssnsbarvj W. E. Formation of 
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23. Black, A. P. Coagulation With Iron Compounds. Jour. Al'Jl'JA, 
26:1?13 (193^) » 

24. Langeliers W. F. and Lud-c-ig, K. F. Mechanitsiri of Flocculation in 
the Clarification of Turbid Waters. Jour a 3MA , 41:i63 (Feb, 1949). 

25. Langelier^ W. F. and Lud.x-jig, E.^ F. Flocculation Phenomena in 
Turbid Water Clarification. Proc.. ASCB , 78slfo. 118 (1952). 

26. Pilinc^Jdchj J. Bo, et al. Elecxrophoretic Studies of Water 
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28. Pacldiam, Re F. The Coagulation Process. III. The Effect of pH 
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30. Stxjirffii, W, and Morgan^ u\ J, Chemical Aspects of Coagulation. 
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31. Black, A. P. and Christman, R, F. Characteristics of Colored , 
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33. Marshall, C. E. and I^rinbill, C. A. The Clays as Colloidal 
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35. Mysels, K» J, In.trod^Q'^-O " ^° Colloid Chemistry , Interscience 
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36. Mysels, K. J. Introductio n to Co?-loid Cheaistry , Interscience 
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3?. Black, A. P. and Willems, D. C-, Slectrophoretic Studies of 
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(May 1961), 

38. Black, A. P. and Christman, R« F. Slectrophoretic Studies of 
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39. PacMiam, R. F. The Coagulation Process - A Reviet-r of Soae Recent 
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pp. 39-42. 

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45. Lvimetron Photoelectric Colorimeter Model 450 for Nessler Tubes. 
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Sulfate. Jouro AWA , In press. 



BIOGRAPHICAL SKETCH 

James Vernon Walters was bom May I3, 1933s 3-t Dublin, Georgia. 
In June, 1951> he was graduated from I>ablin High School. He received 
the degree of Bachelor of Civil Engineering in June, 1955 » from the 
Georgia Institute of Technology. In September of that year he enrolled 
in the Graduate School of the Georgia Institute of Technology. He was 
commissioned in the Public Health Service of the United States in 
November, 1956. His station of duty was the Public Health Service 
Regional Office in Atlanta, Geox'gia. That assignment continued through 
January, 1959. During June, 1958, he received the degree of Master of 
Science, Civil Engineering, from the Georgia Institute of Technology. 

Mr. Walters joined the faculty of the University of Alabama as. 
Assistant Professor of Civil Engineering in February, 1959- He con- 
tinued in that position until September, I96I5 when he x-;as granted 
educational leave to enroll in the Graduate School of the University of 
Florida. From that time until the present, he has pursued his work ■ 
toward the degree of Doctor of Philosopher, 

James Vernon Walters is married to the former Barbara Ann 
Daniell. They have two sons. Mr. Walters is registered in the states 
of Georgia and Alabama as a Professional Engineer and Land Surveyor. 
He is a member of the American Chemical Society, the American Society 
of Civil Engineers, the American Society for Engineering Education, the 
American VJater Works Association, the Water Pollution Conurol Federa- 
tion, the ComiTiissioned Officers Association of the U. S. Public Health 

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Service, the Alabama Public Health Association, the Alabaraa Water and 
Sewage Association, Tau Beta Pi 5 Signia Xi, Chi Epsilon, Alpha Chi SigHia, 
Phi Kappa Phi, and Kappa Kappa Psi. 



This dissertation ^■ra.s prepared iinder the direction of the 
chairman of the candidate's supervisory committee and has been approved 
by all members of that coHnaittee. It was subinitted to the Dean of the 
College of Engineering and to the Graduate Coiincil, and was approved 
as partial falfillment of the requirements for the degree of Doctor of 
Philosophy, 

August 10, 1963 



Dean, College of Engineeringf 



Supervisory Committee: 







Cw^ 



Dean, Graduate School